Conventional plasma CVD systems, for example, are mainly designed to satisfy requirements in the deposition process. A cleaning process for cleaning the inside of the deposition chamber of the plasma CVD system is merely performed as an added step of regulating the deposition process. Further, the deposition chamber is provided with a parallel plate type electrode comprised of a top electrode and a bottom electrode. In the parallel plate type electrodes, high frequency power is fed to the top electrode to generate discharge plasma in the deposition chamber. As a frequency of the above high frequency power, a frequency of 13.56 MHz included in a HF band, which is designated in industrial band specifications, is used. The bottom electrode functions as a substrate holder. A substrate on which a film is deposited is carried on it. Usually, the bottom electrode is attached by a fixed structure. Further, the bottom electrode is usually made by an aluminum alloy or at least a part thereof is treated on it surface with alumite or aluminum oxide. On the other hand, most of the top electrodes are made by the same material as the bottom electrode. In some cases the top electrode is made by pure aluminum.
As a document disclosing the prior art, Japanese Patent Publication (A) No. 10-237657 may be mentioned. The plasma treatment system disclosed in this publication is comprised of a reaction vessel (10: reference numeral used in the publication, same below) provided with a shower head (21) to which the high frequency power is supplied, and a susceptor (2) loading a substrate (70) and raised and lowered by a substrate elevation mechanism (50). The reaction vessel shows the structure in which the shower head (21) is fixed on the chamber (31) through an insulator (41). The insulator (41) electrically insulates the shower head (21) and the chamber (31).
In the development of the recent large-sized plasma CVD systems, priority is being given to the system concept of “raising the efficiency of utilization of the PFC cleaning gas to cut the amount of exhaust”. According to this system concept, the system is being designed to incorporate requirements from the deposition process. Therefore, it is not possible to position the cleaning process of the inside of the deposition chamber as an additional process for the deposition process in the deposition chamber.
In the above plasma CVD system, using the frequency of 13.56 MHz has the advantage of use of an industrial band, but production of high density plasma by a system having the parallel plate type electrode is difficult. This, in particular, has more important meaning in the cleaning process.
According to the conventional plasma CVD systems, the density of the plasma produced between the top electrode and the bottom electrode is low and bias voltage is not applied to the electrodes, so problems do not arise in the top electrode and bottom electrode produced by the above materials. However, if making the density of the plasma higher or applying a high bias voltage to the electrodes, several problems arise in the deposition process or cleaning process or in maintenance of the chamber.
When applying a high bias voltage for PFC plasma cleaning, for example, since the amount of fluorine radicals produced by dissociation of the PFC cleaning gas is large, the problem of corrosion occurs in the entire deposition chamber with the conventional materials or structures.
When producing plasma of high density and depositing a film on the substrate by plasma CVD, the plasma is produced in the narrow space between the top electrode and the bottom electrode. If the inner surface of the deposition chamber is exposed to the narrow space when using plasma for CVD, film will easily deposit on the exposed inner surface. As a result, the problem arises that cleaning will become troublesome and cleaning cannot be efficiently performed.
Further, in the conventional large-sized plasma CVD system, when producing plasma in a wide space for depositing film on the substrate by CVD, the film easily deposits on the entire inner surface of the deposition chamber.
An object of the present invention is to provide a plasma treatment system and a cleaning method of the same which eliminate the problem of corrosion and improve the efficiency of utilization of the cleaning gas so as to reduce the amount of exhaust gas and improve the cleaning efficiency.
Another object of the present invention is to provide a plasma treatment system and a cleaning method of the same which reduce the film deposition on the inner surface of the chamber and improve the cleaning efficiency so as to reduce the amount of process gas used, improve the productivity, and be of help in solving the problem of global warming.